The present invention relates to a pattern inspecting system for detecting defects in an array of the same patterns arranged at a predetermined pitch on a surface of a workpiece and, more particularly, to a pattern inspecting system suitable for inspecting the appearance of semiconductor patterns formed on a surface of a wafer.
When fabricating a semiconductor integrated circuit, such as a large-scale integrated circuit, it is important to detect defects formed in patterns in pattern forming processes and to eliminate the causes of the defects for the improvement of the yield of a semiconductor integrated circuit fabricating system including the pattern forming processes.
The inventors of the present invention proposed a pattern inspecting system capable of automatically detecting defects in semiconductor patterns in Japanese Patent Laid-open No. 59-192943 and this previously proposed pattern inspecting system has been practically used. Principles on which the previously proposed pattern inspecting system is based will be explained. A workpiece, i.e., a semiconductor wafer, is fixedly mounted on a constant-speed movable sample table. The workpiece is moved at a constant speed while a linear sensor disposed perpendicularly to the direction of movement of the workpiece scans the surface of the workpiece and produces image signals. Usually, the same patterns are formed at a predetermined pitch on a semiconductor wafer and, therefore, image signals of the same waveform are produced repeatedly. The image signals are compared with image signals delayed by a time corresponding to the pitch of the patterns. The difference between the image signals is large for parts of the patterns including defects.
The pattern inspecting system based on this principle is capable of detecting defects at a very high defect detecting rate as compared a defect detecting rate at which an operator is able to detect defects. Therefore, the pattern inspecting system has been practically used on semiconductor integrated circuit producing lines as an essential inspecting system. This defect detecting device, however, provides the coordinates of defects as principal defect information. Therefore, it has been necessary to inspect every detected defect visually by means of a reviewing apparatus with reference to a list of the coordinates of the defects provided by the pattern inspecting system to specify the causes of the defects.
Thus the prior art requires the visual inspection of the defects by means of the reviewing apparatus with reference to the list of the coordinates of the defects provided by the pattern inspecting system to obtain necessary data on the defects. Consequently, much time and labor are necessary in addition to time and labor necessary for detecting the defects by the pattern inspecting system to elucidate the causes of the defects. Furthermore, since the visual inspection of the defects needs much time and labor, it is impossible to inspect visually all the defects detected by the pattern inspecting system and only the general condition of causes of the defects could have been estimated from the results of visual inspection of randomly selected sample defects. Consequently, it has been possible that information about serious defects which are formed at a low probability is overlooked.
Accordingly, it is an object of the present invention to achieve quickly the minute analysis of detected defects formed in patterns in a semiconductor pattern forming process by omitting the visual inspection of the defects by means of a reviewing apparatus.
With the foregoing object in view, the present invention provides a pattern inspecting system for quickly detecting defects in patterns comprising a calculating means for calculating characteristic quantities representing the graphical characteristics of defects in synchronism with defect detection, and a classifying means for classifying the defects in clusters by calculated characteristic quantity.
The pattern inspecting system is capable of analyzing the defects. Therefore, the causes of simple defects can be specified through simple defect analysis without requiring visual inspection using the reviewing apparatus. Peculiar defects will not be overlooked, the causes of defects can be quickly specified and the foregoing problems in the prior art can be solved by specifying defects which need visual inspection using a reviewing apparatus.